Full blue channel on HDMI output from skylake above 1920x1080@60Hz

I have a skylake NUC (NUC6i7KYK) which has problems when outputting above 1920x1080@60Hz over HDMI. If I use xrandr to pick any mode at 1920x1080@60 or below, it works fine, but above that it looks like the blue channel is set to full 255 across the screen, including the default output for this display which is 3840x2160@30Hz. It's hard to tell exactly if the other channels are correct or not but they look at least plausibly correct. i.e. the picture is not heavily corrupted otherwise. This is 100% reproducible as far as I can tell, on those resolutions.

This isn't an X specific problem - it starts happening on the tty even if I don't start X, with the tty being white text on a blue background instead of black. I believe it happens as soon as the kernel modeset kicks in, if I disable modeset with nomodeset i915.modeset=0 the picture is fine on the tty, but I then can't start X because /dev/dri/card0 is missing.

I'm not sure what information is relevant for this. Here's the output of dmidecode: dmidecode.txt, dmesg: dmesg.txt, and xrandr --verbose: xrandr.txt

The system info is:

Linux hostname 5.13.13-arch1-1 #1 SMP PREEMPT Thu, 26 Aug 2021 19:14:36 +0000 x86_64 GNU/Linux

Let me know if you need any other information. I'm trying to build a kernel from drm-tip as described in the issue filing documentation, but I'm running into some roadblocks so I'll update with more information if I'm able to do that.

Strangely this works fine on a broadwell NUC I have (NUC5i5RYH) at anything up to 3840x2160@30Hz on the same display over HDMI as well. From that machine dmesg: bw-dmesg.txt, dmidecode: bw-dmidecode.txt, xrandr: bw-xrandr.txt with the same uname info as above. If it's helpful to try and determine the difference between these or test something on both with the same display (I can't use the same cable as the broadwell NUC uses mini-HDMI) I can do that.